July 29, 2010

Recent News from Antarctica

Filed under: Antarctic, Polar

We have featured Antarctica many times in our essay series, and despite a million claims that “the icecaps are melting,” we continue to find no end of articles in major journals building a case for the opposite. Here we examine some recent research, and find evidence for decreased melting and, at least local, mass gains.

The first of our featured articles appeared recently in Antarctic Science by four scientists with various institutions in Chile. Wendt et al. selected a glaciated valley near the Ellsworth Mountains in Antarctica for their study of the ice balance of the area. They note in the beginning of the piece that “The mass balance of the Antarctic ice sheet is receiving increased attention due to its relevance for climate change studies and sea level contribution.” No doubt, and we couldn’t wait to see what they found out.

Wendt et al. used GPS technology to measure the height of the ice from 1996 to 2006; they selected a variety of stakes in the Horseshoe Valley and made relatively precise GPS height measurements at 10 minute intervals over their study period (see Figure 1). To make a long story really short, they found “the best estimation of a thickness change at Horseshoe Valley is 0.05 m a-1 ± 0.002 m a-1. Assuming the determined thickness change on the profile to be representative for the whole valley, we estimate the volume increase to be 0.054 km3 a-1 ± 0.0054 km3 a-1.” If you are metrically challenged, 0.05 m a-1 equates approximate two inches per year. They compare their results to estimates from satellite radar altimetry and note that “These studies indicate a surface height increase between 0.011 m a-1 and 0.024 m a-1 in the region of Horseshoe Valley with errors in the range of few millimetres up to 0.015 m a-1.” In other words, the direct measurements showed more than twice the ice gain than did the more general radar altimetry.


Figure 1. Elevation change rates in Horseshoe Valley derived from comparison between 2006 and 1996 (from Wendt et al., 2009).

There are reasons for the differences and Wendt et al. note “Whereas these [radar altimetry] results are based on large-scale investigations that integrate over a certain area and therefore level out spatial heterogeneities, here we look at a spot measurement in a mountainous region where local effects could predominate. Nevertheless, the statistics approximately agree, suggesting a positive but small elevation change.” We got the message – the local area, at least, is adding ice, not losing ice.

Another recent article in Eos, Transactions, American Geophysical Union (the article is a narrative of the more technical piece published last fall in Geophysical Research Letters) from two scientists with the Cryospheric Processes Laboratory of the City College of New York and the U.S. National Center for Atmospheric Research in Colorado really caught our eye (we featured this finding previously, but bring it up again for its significance). Tedesco and Monaghan begin by noting “Melting over Antarctica has been monitored since 1979 using spaceborne passive microwave observations. The sign of the melting trends over Antarctica is variable at regional scales, depending on the period analyzed and on the indices used, with the continent-averaged trend being negligible.” Negligible???? Melting trends in Antarctica have been negligible? These two scientists better get ready for some serious scrutiny from the IRS or some other enforcement arm of the climate change crusade!

The team notes “During the 2008–2009 austral summer, scientists at the City University of New York and the U.S. National Center for Atmospheric Research observed that snowmelt was at a record low for the 30-year period between 1979 and 2009. Specifically, the Antarctic snowmelt index (the number of days on which melt occurs multiplied by the area subject to melting) in 2008–2009 set a new historical minimum.” They explain further “Negative melting anomalies indicate that melting occurred fewer days than the average over the past 30 years.”

So as you look at their figure below (Figure 2), you will note that the melting index has been unusually low the past three years. The plot also shows the value of the Southern Oscillation Index (SOI) which is basically an index related to El Niño conditions (the index is negative during an El Niño). The Southern Hemispheric Annular Mode (SAM) shown in the figure is a measure of the pressure gradient between the Southern Hemisphere’s middle and high latitudes. The authors perform some analyses that lead them to conclude the recent decline in melting is partially explained by variations in SOI and SAM.


Figure 2. October– January (ONDJ) Southern Hemisphere Annular Mode (SAM) index values (black solid line with diamonds), Southern Oscillation Index (SOI) values (dashed line with circles), and standardized snowmelt index anomalies (gray solid line with triangles). Note that when SAM and SOI are both positive, the melting index is negative (from Tedesco and Monaghan, 2010).

Figure 3 (below) shows the 2009 anomalies and with only one small exception, the entire coastline of Antarctica experienced a low amount of melting – this was widespread and not regionally confined. Claims that Antarctica is melting are simply not consistent with the facts!


Figure 3. Melting days anomalies for 2009 (e.g., difference between the 2009 melting days and the average number of melting days for the past 30 years). Positive anomalies indicate melting lasting longer than the average, and negative anomalies indicate the opposite (from Tedesco and Monaghan, 2010).

It seems like we’ve asked this question a million times before and will probably ask it again a million more times. Had these scientists from these three articles found accelerated melting (or any melting), how many headlines would have covered their stories across the globe? They find a gain of ice mass in the Horseshoe Valley and a historically low amount of melting around the coastlines, so you had to come to World Climate Report to hear all about it.

References:

Tedesco, M., and A.J. Monaghan. 2009, An updated Antarctic melt record through 2009 and its linkages to high- latitude and tropical climate variability, Geophysical Research Letters, 36, L18502, doi:10.1029/2009GL039186.

Tedesco, M. and A.J. Monaghan. 2010. Climate and melting variability in Antarctica. Eos, Transactions, American Geophysical Union, 91, 1-2.

Wendt, A., G. Casassa, A. Rivera, and J. Wendt. 2009. Reassessment of ice mass balance at Horseshoe Valley, Antarctica. Antarctic Science, 21, 505–513.




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